This invention relates generally to the field of scintillation counting, and more specifically to unique devices for reducing the volume of liquid utilized in liquid scintillation counting, and to unique methods for carrying out the scintillation counting operation.
Liquid scintillation counting involves the use of a liquid scintillation fluid comprising a scintillator (e.g., a fluor) carried in a solvent therefor, and a dissolved or suspended radioactive sample to be measured. The radiation emitted as the radioactive atoms of the sample decay interacts with the scintillator to produce fluorescent radiation. This radiation then is measured by a photomultiplier tube and converted to electrical signals that constitute a measurement of the radioactivity of the sample.
The radioactivity of a particular sample commonly is measured as part of an experiment or test to determine other chemically-related information. For example, it is common to measure the radioactivity of a sample in testing to determine the amount of specific chemical in the urine of an animal being treated with a particular type of drug.
It is extremely desirable to use as little of the liquid scintillation fluid as possible in view of the fact that it is costly, volatile, toxic and flammable. Moreover, expensive special procedures may be required to dispose of the fluid in accordance with state and/or federal regulations.
It is quite common in present counting systems to utilize 20 milliliter counting vials which usually are filled approximately halfway with the liquid scintillation fluid. Devices are also available which facilitate the use of smaller amounts of fluid. For example, it is known to use either a rigid or flexible container having less than a 20 milliliter capacity (e.g., a 7 milliliter polyethylene vial) for receiving the fluid. This smaller container then is retained in a holder of approximately the same size as the conventional 20 milliliter counting vial for the purpose of carrying out the measuring operation. By the use of these smaller containers, or vials, the fluid volume used in measuring radioactivity can be reduced by a factor of about 2 to 3, as compared to the volume used in a conventional 20 milliliter vials. However, further reduction has been limited by the required vial geometry inherent in the counting system.
In present liquid scintillation counting systems the measured disintegration rate from the radioactive sample can sometimes be significantly different from the actual, or true, disintegration rate. This can result from a process known as "quenching", which actually reduces the transfer of light energy from the scintillator (e.g., fluor) to the output of the photomultiplier tube(s). Presently available techniques known to Applicant to correct for the effects of quenching all depend upon measuring the light emitted from the scintillation fluid resulting from the interaction of the fluor and either a sample radionuclide, an added radionuclide, or an external radioactive source. In other words, only a single modality has been used in these prior art techniques, that being the light resulting from the interaction of a radioactive sustance with the scintillator in the scintillation fluid.